1. Field of the Invention
The present invention relates to a heat treating apparatus for heat-treating objects to be processed such as semiconductor wafers and, more particularly, to a heat-treating apparatus having a mechanism for loading/unloading the objects to be processed into/from an heat-treating furnace.
2. Description of the Related Art
When, for example, semiconductor wafers are to be heat-treated for oxidation, diffusion, or the like, a plurality of semiconductor wafers, for example 150, are mounted on a quartz boat, and the boat is loaded into a heat-treating furnace to be heat-treated. After heat-treating is completed, the quartz boat on which the semiconductor wafers are mounted is unloaded from the furnace and transferred to a wafer exchange position.
Horizontal and vertical type heat-treating furnaces are used for the heat-treating process. Vertical type furnaces are widely used for the following reasons:
In a heat-treating process, a deposit often adheres to the boat and the interior of the furnace. Therefore, when a horizontal type furnace in which a boat is horizontally loaded/unloaded by an open-side fork is used, the fork may be brought into contact with the deposit which has adhered to the interior of the furnace due to weight of fork, and hence the deposit may drop from the interior surface of the furnace. If the deposit drops in this manner, the dropped deposit may undesirably adhere to a semiconductor wafer as an impurity.
In contrast to this, in a vertical type furnace, since a boat is loaded/unloaded by vertically moving the boat without using a fork, the boat can be loaded/unloaded without bringing the boat into contact with deposits in the furnace. Therefore, the abovedescribed problem does not occur.
When wafers are heat-treated by the vertical type furnace, boats having various lengths are used depending on the number of wafers to be heat-treated. As described above, however, since a boat is loaded/ unloaded from below the furnace body, the apparatus is required to have a height corresponding to at least the total height of the furnace body, the heat-insulating cylinder placed under the boat, and the length of the boat. Therefore, when the height of an installation place is limited, a long boat cannot be used.
Each boat used for heat-treating includes, for examples, four parallel support rods each having a plurality of grooves formed at predetermined intervals, in which a plurality of semiconductor wafers are vertically supported. In the vertical type furnace, while these support rods are vertically set (i.e., wafers are horizontally set), the boat is loaded into the furnace body. The boat is unloaded from the furnace body in the same manner.
The wafers are mounted on the boat at a wafer transfer position which is located in a different area from the heat-treating furnace. Therefore, the boat with the wafers mounted thereon is transferred from this position to the location of the furnace.
Since the boat is loaded into the furnace with the support rods vertically set, as described above, the boat is transferred with the support rods vertically set.